1. FIELD OF THE INVENTION:
The invention relates to a mechanism for stabilizing a well tool in axially concentric relationship to the bore of a well conduit, and particularly to an arrangement for effecting the release of stabilizing elements from a radially expanded position in the event that the stabilizing elements become stuck in the well.
2. SUMMARY OF THE PRIOR ART:
So-called centralizers have long been employed in subterranean wells for positioning a well tool in concentric relationship to the bore of the well conduit. Normally, such stabilizers take the form of a plurality of peripherally spaced, radially outwardly extending leaf spring elements which frictionally engage the bore of the well conduit. With this type of construction, the centralizer necessarily must be in frictional engagement with the well conduit both during run-in and during retrieval of the tool from the well conduit. Such friction not only produces undesirable wear on the centralizer elements but also on the bore wall of the conduit. Moreover, the speed of run-in or withdrawal is necessarily detrimentally affected.
U.S. Pat. No. 4,811,792 discloses a centralizer mechanism comprising a plurality of expandable linkages mounted in a tubular body which can be part of a tubing string or constitute the bottom element of the tubing string. Such expansible linkages carry anti-friction elements, such as rollers, on their outer ends which are movable into engagement with the bore of a surrounding casing. The expandable linkages are normally held in a retracted position during insertion into the well by a shear pin, but are constantly biased to a radially expansible position by a compressed spring. The shear pin preferably comprises a fusible bolt which melts within a short time after running in of the tool string containing the stabilizer elements.
While this mechanism has been generally satisfactory, difficulties are encountered during retrieval of the tool string incorporating such a stabilizing mechanism. If the linkages or the rollers become stuck in the well, for any reason, retrieval of the tool string becomes very difficult. There is a need, therefore, for a stabilizing mechanism incorporating all of the advantages of the mechanism shown in U.S. Pat. No. 4,811,792, but permitting the convenient retrieval of the mechanism in the event that the stabilizing mechanism becomes stuck in the well.